How is transmittance (T) defined in terms of light intensity?

Transmittance (T) is defined as the ratio of the intensity of light transmitted through a material (It) to the intensity of the incident light that strikes the material (I0). This concept is fundamental in understanding how light interacts with matter, particularly in the study of absorption and transmission of light in various mediums.

The formula T = It / I0 clearly indicates that transmittance is a measure of how much light passes through a substance compared to how much light initially hit the substance. If the intensity of the transmitted light is equal to the intensity of the incident light, the transmittance would be equal to 1 (or 100%), indicating that no light was absorbed. If no light is transmitted (meaning all is absorbed), the transmittance is 0, signifying complete absorption.

This definition is crucial in fields such as spectroscopy and photometry, where understanding how materials absorb and transmit light is essential for analyzing samples and determining their properties. The other definitions presented do not correctly represent the relationship between incident light and transmitted light, making the chosen option the accurate representation of transmittance.